Method and apparatus for obtaining a constant predetermined flow of liquid,especially molten metal



April 22, 1969 J. ROUAN-ET ETAL 3,43

IETHOD AND APPARATUS FOR OBTAINING A CONSTANT PREDETERMINED FLOW OF LIQUID, ESPECIALLY HOLTEN METAL Filed Dec. 13. 1966 Sheet of 5 huh-d Fig.1

3,439,759 TERMINED A ril 22, 1969 J. ROUANET ETAL METHOD AND APPARATUS FOR OBTAINING A CONSTANT PREDE FLOW OF LIQUID, ESPECIALLY MOLTEN METAL Sheet Filed Dec. 12, 1966 m h M M A \F Z mm NM v m OM mm mm R m mm (N Apr1l22, 1969 J. ROUANET ET AL 3,439,759

METHOD AND APPARATUS FOR OBTAINING A CONSTANT PREDETERMINED FLOW OF LIQUID, ESPECIALLY MOLTEN METAL Filed Dec. 12. 1966 Sheet Q of 5 April 22, 1969 METHOD AND APPARATUS FOR OBTAINING A CONSTANT PREDETERMINED Filed Dec. 12, 1966 J. ROUANET ET AL FLOW OF LIQUID, ESPECIALLY MOLTEN METAL Sheet of5 v P V F|.4

B A E B4 1 n r 1 April 22, 1969 J. ROUANET ETAL I 3,439,759 METHOD AND APPARATUS FOR OBTAINING A CONSTANT PREDETERMINED FLOW 0F LIQUID, ESPECIALLY MOLTEN METAL Filed Dec. 12. 1966 Sheet 5 of 5 v United States Patent M Int. Cl. ;01g 9/00 US. Cl. 1771v 12 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for obtaining a constant predetermined outflow of liquid metal from a container provided with a calibrated discharge opening in which the level of liquid metal in the container is maintained between an upper and a lower level, in which the time is measured at which the level of the liquid metal in the container drops from said upper to said lower level to thus establish the actual discharge of liquid metal during the time and in which the actual discharge is compared with a reference discharge corresponding to the predetermined outflow and in which in the event a difference is established between the actual discharge and the reference discharge the upper and lower levels of the liquid metal in the container' are changed corresponding to the measured difference.

Background of the invention Various metal refining processes, for instance the production of steel from pig iron are known in the art which are carried out in a continuous manner. One of the main difliculties usually encountered in such continuous refining processes is to obtain a regular and constant flow of liquid metal to be refined into the refining apparatus. This difiiculty is especially encountered in processing ferrous metals due to the high temperature at which these metals .have to be maintained during processing thereof.

It is an object of the present invention to provide for a method and apparatus by means of which a constant predetermined flow of liquid metal into a processing apparatus, for instance a refining apparatus, is obtained even through charge of liquid metal into the apparatus of the present invention is performed intermittently or in an irregular manner.

It is a further object of the present invention to provide for a method and apparatus for the aforementioned purpose in which also variations of the constant flow not caused by the intermittent charging of the apparatus of the present invention can be automatically compensated for.

It is an additional object of the present invention to provide for an apparatus ofthe aforementioned kind which not only operates fully automatically, but which is constructed of relatively few and simple parts so that the apparatus will stand up trouble-free during extended use.

. Summary of the invention With the above objects in view, the method according to the present invention for obtaining a constant predetermined outflow of liquid metal from a container provided in a lower portion thereof with a calibrated discharge opening for discharging liquid metal therefrom mainly comprises the steps of maintaining the level of liquid in the container above the calibrated discharge opening between an upper and a lower limit respectively 3,439,759 Patented Apr. 22, 1969 located at opposite sides of a predetermined mean level by intermittently charging said container with liquid metal, weighing the container and the liquid metal therein at the upper and the lower level and measuring the time between intermittent charges at which the level of liquid metal in the container drops from the upper to the lower limit, comparing the thus established actual discharge during the aforementioned time with a reference discharge corresponding to the predetermined outflow, and charging the upper and lower limit according to a measured difference, if any between the actual discharge and the reference dis charge.

The method may also include the step of compensating anyslow deviations of the actual discharge from the desired discharge due to wear of the calibrated discharge opening, variations in the temperature of the metal, etc., by changing the upper and lower limit of the liquid level in the same direction.

The apparatus for carrying out the above method of the present invention mainly comprises a container provided in a lower portion thereof with a calibrated discharge opening for discharging liquid metal from the container, charging means for intermittently charging the container with liquid metal at a rate motably greater than the rate of outflow of liquid metal from the container through the calibrated discharge opening, the charging means including operating means for starting and stopping discharge of liquid metal from said charging means into the container, automatic weighting means cooperating with the container for weighing the latter and the liquid metal therein, the automatic weighing means including two members respectively adjustable to predetermined upper and lower weight limits and cooperating with the operating means of the charging means for automatically starting discharge of liquid metal from the charging means into the container when the weight of the container and the contents therein drops at least to the lower weight limit and for automatically stopping discharge of liquid metal into the container when the weight of he latter and the contents therein rises at least to the upper weight limit, adjusting means comprising calculating means for calculating the amount of liquid metal actually discharged from the container during two subsequent chargings thereof from the charging means, comparator means for comparing the calculated actual discharged amount of liquid metal with a reference value corresponding to the desired discharge, and means cooperating with the comparator means for changing the position of the adjustable members in-accordance with the difference, if any, between the calculated discharge and the reference value.

The calculator means may include a chronograph measuring the time required for liquid metal equal to the difference between the upper and the lower weight limit to flow out through the discharge opening.

The charging means may comprise a storage container for liquid metal arranged above the first-mentioned container and provided with an outlet opening and stop means movable between a rest position closing the outlet opening for stopping flow of metal therethrough and an open position permitting flow of metal through the outlet opening from the storage container in the first-mentioned container, and moving means connected to the stop means and cooperating with the adjustable members of the automatic weighing means for moving the stop means between the positions thereof.

The present invention aims to obtain a constant and adjustable discharge of liquid metal and it has also the advantage to permit to measure and to regulate the discharge to a desired value.

While it is especially important to provide for a constant flow of liquid metal or a flow of liquid metal which can be adjusted to a desired value in continuous metal refining processes, there are also other continuous processes for which obtainance of the above results is important, for instance, continuous metal casting processes.

The method according to the present invention is not only applicable to molten metals but also to other liquid material, it is of interest in all such cases in which the usual methods of regulating and measuring the discharge of a liquid cannot be used due to the high temperature or due to the aggressive nature of the liquid in question.

The method according to the present invention is based on the well-known law that a constant discharge will take place from a discharge opening of a container in which a constant level of liquid is maintained. While this basic principle is simple, it is diflicult to apply the same in actual practice, especially with molten metals, since. it is extremely difficult to maintain a constant liquid level in a container while liquid flows continuously out therefrom. In addition, maintaining the level of liquid constant in a container does not by itself permit to actually measure the amount of liquid discharge, nor does this permit to compensate for variations in certain parameters influencing the discharge, as for instance the temperature of the metal, the wear in the refractory lining'of the container or change of the cross-section of the discharge opening due to wear, etc.

The invention essentially consists in maintaining the level of the liquid in the container between two limits respectively located to opposite sides of the above-mentioned constant level by adding a quantity of liquid metal when the liquid level in the container reaches its lower limit so as to raise the liquid level again to the upper limit. The upper and lower limits are chosen sufliciently close to each other so that the liquid level does not vary greatly,

and in actual practice it has been found that a variation of about 10% of the height of the liquid metal above the discharge opening works out satisfactorily. The discharge will therefore proceed with cyclical variations as a function of the liquid level in the container and it has been proven that in this way a mean discharge is obtained which, if all other parameters influencing the discharge are maintained constant, will depend only on the mean level of liquid in the container. The actual discharge of liquid metal is measured by weighing the container and the contents therein between the two liquid levels while no additional charge of the container with liquid metal takes place. Actually, it is not possible to measure the discharge of liquid metal from the container while the latter is simultaneously charged with additional metal. it is pointed out that the dynamic effect of the jet of liquid metal during the charge of the container would disturb an exact measurement of the weight of the container and the metal therein, and therefore it has been found preferable to measure the discharge of metal from the container only during the periods at which the liquid level drops from its upper to its lower limit, so that the measurements are not affected by the disturbance in the mass of liquid in the container by the intermittent jets which feed new liquid into the container.

From the above it will be evident that actual measurement of the mean discharge of the liquid metal from the container is carried out according to the present invention only during a fraction of time, which can cause a certain inaccuracy in determining the total mean discharge. To reduce the inaccuracy, the various elements of the apparatus according to the present invention are constructed to increase as much as possible the aforementioned fraction of time. Evidently, the greater the speed at which the liquid metal is fed intermittently into the container, the greater 'will be the fraction of time during which the discharge of liquid metal from the container can be measured. During actual tests, the aforementioned fractions have been varied between 0.6 and 0.95.

Slow deviations from the mean discharge due to variations of other factors which influence the outflow of the liquid metal from the container can be compensated for by a corresponding change of the mean level of liquid metal in the container. Such factors which influence the discharge of liquid metal from the container may for instance be variations in the temperature of the liquid metal, wear of the refractory lining of the container and wear of the discharge nozzle, variations in the composition of the metal, etc. These factors are compensated for by comparing the measured discharge with the desired discharge and :by simultaneously changing the upper and lower level of the liquid metal in the container without changing the diiference between the two levels in the event a difference is ascertained between the measured discharge and the desired discharge. In this way all causes of slow deviations from the desired mean discharge may be compensated for, even if the causes of these deviations are unknown.

In a preferred form for carrying out the method .according to the present invention the upper and lower liquid levels in the container are replaced by upper and lower weight limits which are easier to establish since there exist presently many mechanical and electronic weighing apparatus suitable for exactly weighing a container for liquid metal and the contents thereof, and such weighing apparatus may be provided with adjustable marks and control elements, for example electrical contacts which are opened or closed, respectively, when the measured weight reaches an upper or a lower weight limit. In this way it is possible to carry out fully automatically, by means of impulses imparted by the contacts, all weighing operations, control of successive charges of the container, and corrections of the mean level of liquid metal in the container.

It is to be understood that the method according to the present invention can be carried out also in different ways. For instance, it is also possible to pour into the container a fixed amount of liquid metal in regulated time intervals, in which the amount of metal which is poured each time into the container and the intervals be tween successive charges are chosen in such a manner that the level in the container between successive charges does not vary too much, for instance not more than 10%. In this modified method the mean discharge is determined by the frequency of successive charges and the quantity of liquid metal poured during each charge in the container and the mean level in the container establishes itself automatically at a value resulting from the equilibrium between the charges and the outflow of liquid metal from the container. However, this modified method, which at first glance appears very simple, is not very advantageous since the amount of metal poured during each charge into the regulating container can be determined only by weighing the charging container and the contents from which the metal is poured and which is usually of large size, which is not advantageous from the standpoint of exact measurement, or by using a small intermediate container, which is not advantageous from the standpoint of thermal losses.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will vbe best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

Brief description of the drawing FIG. 1 is a schematic cross-section through an apparatus for carrying out the method of the present invention.

FIG. 2 is a schematic diagram of the elements of the apparatus for carrying out an automatic weighing operation;

FIG. 3 is a schematic partially sectioned view and showing the wiring diagrams of the elements controlling the automatic charges of the control container;

FIG. 4 is an explanatory diagram explaining the functionof the apparatus;

FIG. 5 illustrates an experimentally established curve of discharge of liquid metal from the container; and

FIG. 6 is a diagrammatic view completing the diagrammatic views of FIGS. 2 and 3 and showing another embodiment in which the control arrangement includes a numerical calculator.

Description 07 the preferred embodiments FIG. 1 schematically illustrates an apparatus according to the present invention adapted to furnish to a refining apparatus of known construction, which is not illustrated in the drawing and which does not form part of the present invention, a constant flow of liquid metal. The apparatus includes a container .1 similar to a ladle used in steel plants, provided with a refractory lining 2 and acalibrated discharge opening or nozzle 3. The container has a greatly flaring conical shape so that the surface of the liquid bath at which level variations will take place is large while the total, capacity of the container is relatively small. In this way the influence of level variations'on the total weight are increased and thereby the exactness of the weight measurement.

The metal 4 in the container 1 flows through the nozzle 3 in a jet 5 which drops into a receptacle 6 from which it flows continuously through a channel 7 in an apparatus of use not illustrated in the drawing.

-The container 1 is supported on three strain gages 8 of a weighing apparatus, displaced through 120* from each-otherand only two of-which are shown in FIG. 1, which in turn rest on beams 9 forming part of a frame structure only partially illustrated in FIG. 1. The strain gages-8 are connected to a measuring bridge of known construction which will be described in further detail later on.

'A storage container or ladle 11-1 of great capacity is arranged above the container v1 and provided with an outlet opening or nozzle 12 and stop means in the form of a stopper rod 13 movable between a rest position closing the outlet opening for stopping flow of liquid metal from the container 11 into the container 1, and an open position, as shown in FIG. 1, permitting flow of metals through the nozzle 12 into the container 1. The stopper rod '13 is moved between the positions thereof by a hydraulic jack 14 having a piston rod 15 connected by a transverse arm to the stopper rod 13. Pressure fluid is fed into and'out from the hydraulic jack through conduits 14a "and 14b and flow of fluid through theseconduits is controlled in the manner as will be described'later on.

The container 1 has at an upper portion thereof an asymmetric projection in the form of a beak '16 projecting to one side of the container and arranged beneath the nozzle 12 so asto receive the jet of liquid metal .17 dischargedthrough the nozzle 12 of theladle 11. In this way disturbance of the massof metal 4 in the ladle 1 and of the jet '5 by the jet 17 impinging onto the liquid metal in the ladle 1 is greatly diminished.

' In order to obtain an outflow of liquid metal of about 500 kg. per minute from the ladle "1, the latter has a capacity of .2r-2.5 tons and a nozzle with an inner diameter of 36 mm. The supply container :11 has a capacity as great as possible, for instance 30 to 50 tons.

The function and arrangement of the control elements for automatically controlling intermittent charges of the container 1 will now be explained with reference to FIG. 2.

The weight of the container 1 and the contents thereof is measured by an automatic extensometer bridge of known construction provided with the aforementioned three strain gages 8 which are indicated in FIG. 2 by a single strain gage 8a. The bridge 10 is an ele-ctromechanic registering bridge, the carriage of which moves an indicator 18 and a registering pen connected thereto. Since according to the present invention it is only necessary to measure weight variations, the scale is constructed to indicate variations from a base Weight of about 2.5 tons and the extension of the scale is equal to 1000 kg. which increases the precision of the regulation obtainable and which facilitates reading of the scale. The weighing apparatus is provided with four members or index marks 19a, 19b, 19c and 19d which are adjustable along the scale, and each of which is constructed in a known manner to control -a respective one of electric contacts 20a, 20b, 20c and 20d. The aforementioned contacts are for clarity sake shown in FIG. 2 respectively above the corresponding index marks. The arrangement is made in such a manner that each of the contacts is closed when the movable pointer 18 of the weighing apparatus indicates a weight inferior to the weight on the scale respectively marked by the adjustable index marks 19a- 19d, that is when the pointer 18 is to the left of the respective index mark, while the respective contact is opened in the contrary case.

The extreme contacts 20a and 20d form a part of a control circuit as illustrated in FIG. 3. The contacts 20a and 20d are connected in series with the exciter coil of an electromagnetic relay 21 and a source of current 22. The contact 20a is connected to a holding contact 21a of the relay, which holding contact is closed when the relay is excited. The contact 21b of the relay is likewise closed when the relay coil is excited and this contact when closed will energize the magnet coil 23a of a distributor valve 23.

The above-described arrangement will operate as follows:

At the start of the operation the container 1 is empty and the pointer 18 of the weighing apparatus is located at the extreme left end of the scale, the contacts 20a and 20d are closed, the relay 21 is excited, which in turn causes closing of the contacts 21a and 21b and excitation of the coil 23a of the distributor valve 23, which will cause movement of the pistons 23b and 23c of the distributor valve towards the left, as viewed in FIG. 3, against the force of a spring 26 so that liquid under pressure may flow through a conduit 24 from a source of liquid under pressure, not illustrated in the drawings, into the conduit 14b beneath the piston of the hydraulic jack 14 while pressure fluid above the piston of the hydraulic jack may flow through the conduit 14a into a discharge conduit 25b of the distributor valve 23. The piston rod 15 is thereby moved in upward direction to lift the stopper rod 13 to the position shown in FIG. 1 so that liquid metal from the storage container 11 will flow out from I the latter through the nozzle 12 into the container 1. The

weight of the liquid metal flowing into the container 1 will cause movement of the pointer 18 of the weighing apparatus from its left end position towards the right, as viewed in FIG. 2. When the pointer 18 passes the index mark 19a the contact 20a will open, but this opening will not produce any change due to the holding contact 21a. After the pointer 18 reaches the index mark 19d, the corresponding contact 20d will open, the relay 21 will become deenergized, opening contact 21b and causing disconnection of the coil 23a, so that the pistons 23b and' 23c will return under the influence of the spring 26 to the rest position shown in FIG. 3. Pressure fluid is now fed-through the conduit 14a above the piston of the hydraulic jack 24, while pressure fluid below the piston will flow out through the conduit 14b and the discharge conduit 25b. The piston rod 15 and the stopper rod 13 are thereby lowered and further discharge of liquid metal from the storage container 11 is interrupted. Since metal is continuously discharged from the container 1, the pointer will gradually return toward the index mark 19a and when the pointer 18 passes the index mark 19a again, the contacts 20a and 20d are closed and the aforementioned cycle is repeated.

The measurement and the regulation of the discharge from the container 1 is etfectuated by means of the index marks 19b and 190 located between the index marks 19a and 19d.

For a discharge of 500 kg. per minute the spacing between the index marks 19a and 19d corresponds to 375 kg. on the scale, while the spacing between the index marks 19b and 19c corresponds to 300 kg. on the scale, which leaves at each extremity of the scale, respectively between the index marks 19a and 19b and between the index marks 19c and 19d a space corresponding to 37.5 on the scale between which no measurement of the discharge takes place in order to avoid, as mentoned above, disturbances of these measurements due to the influence of the jet 17.

It is mentioned that the influence of thrust of the continuous jet has been experimentally studied and it has been ascertained that this jet has practically no influence on the exactness of the measurement.

The contacts 20b and 200 control the synchronization circuit of a relay 27 (FIG. 2) which in turn controls a series of measuring and regulation actions in the manner as will now be explained.

The circuit of relay 27 is not illustrated in detailed manner in order to simplify the drawing and the description, but this circuit can be easily visualized by any person skilled in the art on the basis of the following explanations. The circuit essentially comprises two relays, closing of which is controlled by the closing of the contacts 20b and 20c, and these two relays are called in the following description as starting relay and stopping relay.

A clockwork 28 producing successive impulsions, for instance ten impulsions per second, is started by closing of the starting relay and stopped by closing of the stopping relay. The number of impulsions emitted are counted by a counter 29 which indicates in this way directly the time necessary for discharging 300 kg. of liquid metal through the jet 5. The counter 29 is calibrated according to the mean discharge expressed in kg.s per minute. The impulses emitted by the clockwork 28 are likewise furnished to an integrator 30 constructed to deliver a continuous tension proportionate to the number of impulses received, and this continuous tension is compared with a reference tension delivered from a manually adjustable device 31 and graduated directly in kg.s per minute by a comparator circuit 32. The comparator circuit 32 delivers the difference between the two tensions, if there is any difference, into a memory circuit 33 which registers the amount of any difference existing between the two tensions. After the count is completed, that is when the stopping relay closes, the same relay acts on the memory circuit 33 and causes application of the registered tension difference to a control amplifier 34 which controls a small servo motor 35 to displace the index marks 19a-19d along the scale without changing the spacing between these index marks. The servo motor 35 drives also a tachometer generator 36 which produces a voltage proportionate to the speed of the motor and which is applied to the memory device 33 in reverse direction to the voltage difference applied thereto from the comparator 32. Thus, when a voltage difference is ascertained, the servo motor 35 displaces the index marks 19a-19d until the voltage delivered by the generator 36 and integrated by the memory device 33 has canceled the registered voltage difference, which will cause a total displacement of the index marks 19a-19d proportionate to the ascertained voltage difference. It is to be understood that the displacement of the index marks occurs in a direction which tends to correct the ascertained deviation, that is the index marks are displaced towards the right, as viewed in FIG. 2, when the weight of the liquid metal discharged from the container 1 is inferior to the weight to which the device 31 is set, and vice versa.

During charging of the container 1 and return movement of the pointer 18, the clockwork 28 remains in operation; however, this remains without consequence since the memory device 33 is during this time locked by opening of the stopping relay. During the following cycle, the above-described sequence of operation is repeated in the same manner.

To change the amount of liquid metal delivered by the apparatus according to the present invention it is therefore only necessary to change the value of the voltage imparted to the circuit 32 by the device 31 within the practical limits resulting from the actual construction of the apparatus illustrated in FIG. 1.

FIG. 4 is a diagram illustrating the function of the apparatus. In the diagram the weight P of the container 1 and its contents and the mean discharge Q of the liquid metal from the container 1 are illustrated as a function of time. The saw-tooth-shaped curve A represents the weight of the container 1 and its contents after a starting period. The periods of measurement of the discharge are cross-sectioned in FIG. 4, neglecting the neutral intervals between the index marks 19a, 19b, and 19c, 19d, respectively. The weight oscillates between the limits represented by the horizontal lines B and C. The mean discharge of liquid metal is represented by the dotted lineD. During the measuring period E a lowering of the discharge has been ascertained, and the limits B and C are raised to the limits B and C in order to correct the reduced discharge.

FIG. 5 illustrates experimentally established curves showing the results obtained with the' method of the present invention. The curve F illustrates the measured discharge as a function of time. The measuring points of this curve are spaced about 45 seconds from each other. This curve shows the remarkable constancy of the discharge obtained with the method according to the present invention. Any factor tending to cause a variation of the discharge is rapidly corrected.

The dotted curve G illustrates the values of the coefi'icient:

pSV 29h during the same period, calculated from the measured discharge and the medium height of liquid metal in the container 1 at any moment. In the above formula, p is the density of the liquid metal, S the cross-section of the nozzle 3, g the acceleration due to gravity, and h the height of liquid metal in the container. From the curve G it can be seen that the coeflicient K varies between 0.75 and 0.9, which would have caused in the absence of corrections produced with the apparatus of the present invention corresponding variations in the discharge of liquid metal from the container 1.

Following is a description of a modified apparatus which includes a numerical calculator or computer. While such a numerical calculator is rather expensive, modern manufacturing methods use increasingly completely automatic processes, and therefore the use of a calculator as accessory to the apparatus of the present invention in order to arrive at an automatic process is often advisable. This is, for instance, the case in an installation for the continuous refining of pig iron into steel.

This modification will now be explained with reference to FIG. 6 in which a calculator 37 is schematically indicated which may for instance be used with the aid of non-illustrated means to control and to carry out in a fully automatic manner a continuous refining process of pig iron into steel by means of blowing of oxygen. The continuous refining process may be carried out in any manner whatsoever and this refining process is not described since it does not influence in any way the process according to the present invention. The process according to the present invention serves to regulate a chosen constant discharge of pig iron into a continuous refining apparatus.

The calculator 37 receives continuously indications of the weight of the container 1 and the contents thereof coming from the weighing apparatus or the registering bridge 10 through an intermediate analog/ digital converter 38 of known construction. On the other hand the calculator 37 can send by means of a control device 39 of known construction connected thereto control signals for energizing and deenergizing the coil 23a of the distributor valve 23 to thus startand stop flow of liquid metal from the storage container 11 into the container 1. The calculator 37 elaborates the opening and closing orders and de termines the metal discharged from the container 1 by carrying out a series of calculations described below.

The calculator receives the ordered discharge (the desired discharge Q in digital form from an adjustable device 40 attached thereto.

At the start of the operation the calculator 37 determines the height of liquid level in the container 1 in principle necessary to obtain the desired discharge Q according to the formula:

which formula g is the acceleration due to gravity, h the height of the liquid metal above the nozzle 3, and a is a coeflicient of outflow which depends from the form of the container, the density and viscosity of the metal therein, the cross section of the nozzle, etc. The coeflicient a is experimentally determined during preceding pourings from the apparatus of the present invention. Any way, it is sufficient to establish the first time only an approximate value of this coefficient since its correction is subsequently automatically carried out in the manner as will be described below.

The calculator is constructed to determine from the known geometric characteristics and dimensions of the container 1 the weight of the metal P corresponding to the height of h metal bath in the container and to calculate the total weight by adding the weight of the empty container to the calculated weight.

Subsequently thereto the calculator fixes the lower and upper weight limits in order to carry out the method of the present invention, for instance these limits are fixed at 0.95 P and 1.05 P and it controls opening of the stopper rod 13 until the weight of the metal in the container 1 is equal to 1.06 P After moving of the stopper rod 13 to the closed position the calculator measures the time necessary for the weight of the metal to pass from 1.05 P to 0.95 P and calculates therefrom the actual discharge Q of molten metal from the container 1 and compares the actual discharge Q with the desired discharge Q If a difference is ascertained, the calculator solves the equation and determines therefrom the actual value of a and subsequently thereto a new value h for the height of the metal in the container 1 corresponding to the desired output Q When the weight of the metal in the container 1 drops to 0.94 P, the calculator issues a control signal which causes reopening of the stopper rod 13 and the cycle is repeated with a new value P for the weight.

In this way, the calculator corrects for each cycle the coeflicient a which varies in an unknown manner under the influence of various factors such as for instance the temperature of the metal, wear or partial clogging of the nozzle 3, etc., to thus in this way assure a perfect constancy of the mean discharge of liquid metal from the container 1.

From the numerical values given above, it will be noted that control of the charge of the container 1 is made according to weight limits set at 0.94 P and 1.06 P, while I the measurement of the discharge is made between narrower limits, that is between 0.95 and 1.05 P. Therefore there exist four distinct limits. As in the preceding example this way of measuring is devised to avoid disturbance of the exact discharge measurement by the jet 17 by providing at each extremity of the measuring interval a space at which no measurement takes place.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. A method for obtaining a constant predetermined outflow of liquid from a container provided in a lower portion thereof with a calibrated discharge opening for discharging liquid therefrom, comprising the steps of maintaining the level of liquid in the container above said calibrated opening between an upper limit and a lower limit, respectively located to opposite sides of a predetermined mean level, by intermittently charging the container with liquid; weighing said container and the liquid therein at said upper and at said lower level and measuring the time between intermittent charges at which the level of liquid in the container drops from said upper to said lower level; comparing the thus established actual discharge during said time with a reference discharge correspondent to said predetermined outflow, and changing said upper and said lower limit according to a measured difference, if any, between said actual discharge and said reference discharge.

2. A method as defined in claim 1, wherein said level of liquid is maintained by automatically starting feeding of liquid in said container when the weight of said container and its contents is at a Weight corresponding substantially to said lower level and by automatically interrupting feed of liquid into said container when the weight of said container and its contents is a weight corresponding substantially to said upper level.

3. A method as defined in claim 1, wherein said distance between said upper and said lower level is about 10% of the distance between said mean level and said discharge opening.

4. A method as defined in claim 1, and including the step of compensating slow deviations of the mean discharge due to Wear of said calibrated discharge opening, change of the temperature of the liquid, etc., by changing said upper and said lower level in the same direction.

5. A method as defined in claim 1, wherein said liquid is molten metal.

6. Apparatus for obtaining a constant and predetermined flow of liquid metal comprising, in combination, a container provided in a lower portion thereof with a calibrated discharge opening for discharging liquid metal from said container; charging means for intermittently charging said container with liquid metal at a rate notably greater than the rate of outflow of liquid metal from said container through said calibrated discharge opening, said charging means including operating means for starting and stopping discharge of liquid metal from from said charging means into said container; automatic weighing means cooperating with said container for weighing the latter and the liquid metal therein, said automatic weighing means including two members respectively adjustable to predetermined upper and lower weight limits and cooperating with said operating means of said charging means for automatically starting discharge of liquid metal from the charging means into said container when the weight of the container and the contents therein drop at least to said lower weight limit, and for automatically stopping further discharge of liquid metal from said charging means into said container when the weight of the latter and the contents therein rises at least to said upper weight limit; adjusting means comprising calculator means for calculating the amount of liquid metal actually discharged from the container between two subsequent chargings thereoif from the chargings thereof from the charging means, comparator means for comparing the calculated actually discharged amount of liquid metal with a reference value corresponding to 1 1 the desired discharge, and means cooperating with said comparator means for changing the position of said position of said adjustable members in accordance with the difference, if any, between the calculated discharge and said reference value.

7. An apparatus as defined in claim 6, wherein said calculator means comprises a chronograph measuring the time required for liquid metal equal to the difference between said upper and said lower weight limit to flow out of said discharge opening.

8. An apparatus as defined in claim 6, wherein said calculator means comprises a calculator for calculating at any instant the necessary level of liquid metal in the container for obtaining a desired discharge as a function of the outflow coefficient of said discharge opening.

-9. An apparatus as defined in claim 6, wherein said charging means comprise a storage container for liquid metal arranged above said first mentioned container, said storage container having an outlet opening, stop means movable between a rest position closing said outlet opening for stopping flow of metal therethrough, and an open position permitting flow of metal through said outlet opening, and moving means connected to said stop means and cooperataing with said adjustable members of said automatic weighing means for moving said stop means between said positions thereof.

10. An apparatus as defined in claim 9, wherein said outlet opening of said storage container is arranged laterally from said discharge opening in said first mentioned container.

11. An apparatus as defined in claim 10, wherein said first mentioned container is an open vessel having an inner surface tapering from the upper to the lower end of said vessel, said vessel having at an upper portion thereof an extension projecting to one side thereof, and said outlet opening of said storage container being located above said extension.

12. An apparatus as defined in claim 9, wherein said stop means comprise a stopper rod, and said moving means includes cylinder and piston means connected to said stopper rod for moving the same between said positions thereof.

References Cited UNITED STATES PATENTS 2,728,123 12/1955 Jordan 222-56 3,256,947 6/1966 Fiedler et al l77-1 3,285,276 11/1966 Schipper 137-408 RICHARD B. WILKINSON, Primary Examiner.

G. H. MILLER, JR., Assistant Examiner.

U.S. Cl. X.R. 

